Relatively little is known about the cellular mechanisms involved in pepsinogen secretion from chief cells. A major obstacle has been the lack of a preparation that is homogeneous in its chief cell content and responsive to stimulation. Recently, the principal investigator has developed methods for preparing dispersed chief cells from guinea pig stomach that are responsive to secretagogues. Chief cells constitute 90% of the final cell suspension and 5-fold stimulation of pepsinogen secretion is observed with secretagogues whose actions are probably mediated by cyclic AMP (secretin) or calcium (carbamylcholine, cholecystokinin). In the present research plan we proposed to use this preparation to measure directly the effect of various secretagogues on cellular calcium and cyclic AMP. Cellular calcium fluxes will be measured by loading dispersed chief cells with 45Ca, incubating with secretagogues, and measuring cellular radioactivity. Cellular cyclic AMP will be measured by incubating dispersed chief cells with secretagogues and measuring cellular cyclic AMP by radioimmunoassay. To establish the relation between these cellular events and enzyme secretion, cells will be incubated under conditions similar to those above and pepsinogen secretion will be measured. By relating changes in enzyme secretion from dispersed chief cells to changes in cellular calcium and cyclic AMP, it will be possible to establish the role of these cellular mediators in pepsinogen secretion. If successful, these studies will elucidate the cellular mechanisms of pepsinogen secretion. Moreover, by examining the effect of combinations of secretagogues on pepsinogen secretion in relation to changes in cellular calcium and cyclic AMP it may also be possible to determine the cellular basis for potentiating interactions between secretagogues. These studies have implications regarding the mechanisms of peptic ulcer disease and might suggest methods for inhibiting pepsinogen secretion in this disorder. Furthermore, because similarities have been noted between pepsinogen secretion from chief cells and enzyme secretion from other tissues, these studies will be important for understanding cellular mediation of enzyme secretion in a variety of tissues.